} CAS: Teachers - Taxonomist for a Day

Teachers > Lessons & Kits > Lesson Plans > Connected Experience: Taxonomist for a Day

Connected Experience: Taxonomist for a Day


In this activity, students will  use a dichotomous key to identify animals, observe biodiversity and begin to understand its importance, learn about a few of the animals that live in the California coastal marine environment, and think about how scientists classify organisms


In this activity, students will:

  1. learn about dichotomous keys
  2. use a dichotomous key to identify animals
  3. observe biodiversity and begin to understand its importance
  4. practice making close observations
  5. learn about a few of the animals that live in the California coastal marine environment
  6. start to think about how scientists classify organisms


  • Key to the Animals of the California Coast Exhibit
  • Taxonomist for a Day worksheet
  • Set of California Coast Exhibit animal photos
  • Guess Who Game Cards
  • cardstock
  • scissors or paper cutter
  • Identifying Animals in the California Coast powerpoint
  • projector
  • colored pencils/crayons (optional)


  • dichotomous key: in biology, keys are used to identify a biological specimen to a certain level of classification, such as an order, family, genus or species. The key is organized into several couplets.
  • couplet: a set of mutually exclusive, descriptive statements in a dichotomous key.  Each statement in a couplet leads to another subsequent couplet until the identification is reached.
  • invertebrate: animal without a backbone
  • systematics: the study of the diversity of life, both past and present, and the evolutionary relationships among living things through time.
  • identification: the process of assigning specimens to names
  • taxonomy: the science of identifying, naming, describing and classifying organisms
  • taxa: plural of taxon, a grouping of organisms at any level in the systematic hierarchy (e.g. species, genus, family)

Vocabulary for key

  • fin: a flattened appendage of an aquatic animal used in locomotion or maneuvering in the water.
    • Tail/Caudal fin: a fin at the posterior extremity (rear end) of a fish's body, typically continuous with the tail.
    • Dorsal fin: an unpaired fin on the back of a fish or whale, e.g., the tall triangular fin of a shark or killer whale.
    • Pelvic: each of a pair of fins on the underside of a fish's body, attached to the pelvic girdle and helping to control direction.
  • tentacle: a slender flexible limb or appendage in an animal, especially around the mouth of a marine invertebrate, used for grasping, moving about, or bearing sense organs.
  • column: in anemones, the cylindrical part of the body between the tentacles and the substrate it attaches to.
  • spine: any hard, pointed defensive projection or structure, such as a spike-like projection on a sea urchin.
  • gill: an organ used by aquatic organisms for gas exchange in water.
  • symmetry:
    • bilateral: the property of being divisible into halves that are mirror images of each other on either side of an imaginary line, i.e., having two sides.
    • radial: a body shape in which the parts of an animal are arranged in a circle around a central axis, and more than one imaginary line through this axis yields halves that are mirror images of each other.


Before your visit

Part I. Introduction

Begin by playing a game of “Guess Who?” 

This game is modeled after the game “Guess Who?” by Milton Bradley.  In this version, the cards have images of different animals that can be found in the waters off of the California coast. Each animal is also found on the Key to the Animals of the California Coast Exhibit, which will be explored in Part II. 

Similar to “Guess Who?” the object of the game is to guess your opponent’s Mystery Animal.  Students will use process of elimination to guess their opponent’s animal by asking a series of “yes” or “no” questions. This activity will help students to practice making close observations of these animals, and begin thinking about ways to divide the organisms into different groupings or classifications based on similar characteristics.  


Each pair or group of students that plays a game of “Guess Who?” will need to have a deck of cards.  Each deck consists of a total of 36 cards.  To create a single deck, print out two copies of each page of the pdf file on cardstock.  You may cut out the cards yourself ahead of time with a paper cutter, or have your students cut out the cards with scissors before playing the game.

Please note: If you do not have access to a color printer, print out the black and white version of the cards, and have your students color in the images according to what you see on the color version pdf.


  1. Have students work in pairs or groups of four. The rest of the procedure describes play for 2 players. If students are playing in groups of four, have the groups divide into two teams that will compete against each other during the game.
  2. Each pair of students should receive a deck (see Preparation section above for what constitutes a deck).  Each pair should split up the deck so that each player receives a "set" of cards (half the deck) that contains two images of each animal, one with a thick border, and one without. 
  3. Once the deck has been split properly, have students look at the animals on the cards and record observations.  For example, some of the animals have fins, some have spines, some are fish, some are invertebrates, some are different colors, etc.
  4. Each pair of students should work together to brainstorm questions that they can ask each other during the game.  It is also a good idea for students to clarify within their pairs what they consider to be spots, or colors, or eyes, etc, on the cards so that there is minimal confusion during game play.
    Gameplay (Adapted from “Guess Who?” by Milton Bradley)
    Cards with thick borders- Select ONE animal from the cards with the thick border.  Do not share the identity of your card with your opponent.  This is the animal that your opponent will have to guess by asking you a series of “yes” or “no” questions.  Once you choose your animal, put aside all the rest of the cards with a thick border.  For the rest of the game, you and your opponent will be using the border-less cards to keep track of the answers to the “yes” or “no” questions you ask.   Hold these cards in your hand and discard them as you eliminate possibilities.
    Determine who will go first by flipping a coin or choosing the youngest player.
    Your turn- On your turn, you may either ask a question, or guess who the Mystery Animal is.  Don’t use your turn to guess the Mystery Animal until you are ready!  If your guess is wrong, you lose the game.
    Asking questions- Ask your opponent one question per turn.  Each question must have either a “yes” or “no” answer.  After your opponent answers, you may be able to eliminate one or more of the border-less cards.  For example, you may ask “Does your animal have a tail?”  If your opponent answers “yes,” then you should discard all cards in your hand except for the ones with a tail.   If your opponent answers “no,” then you should discard all cards except for those without a tail.  After you discard your cards, it is your opponent’s turn.  You and your opponent will alternately take turns asking the questions.
    Guessing the Mystery Animal-Once you are ready to guess what the Mystery Animal is, make your guess on your turn instead of asking a question.  For example, you might guess “Your animal is the purple sea urchin.” If the answer is correct, then you win and the game is over. However, you should give the other player a chance to finish asking their questions and guess your animal.  If your guess is wrong, then your opponent wins the game.
  5. Explain to students that their answers to questions must be based ONLY on what they can see in the picture.  This will level the playing field in case any students have more knowledge regarding the animals on the cards. 
  6. Have students play “Guess Who?” for several rounds so that they may try guessing many animals (about 15-20 minutes). 
    Note: In “Guess Who?” each question must be a “yes” or “no” question.  With dichotomous keys, not each couplet is necessarily a “yes” or “no” question, but each couplet will have statements that are mutually exclusive (e.g the animal is either blue or red). 

Wrap up

Discuss the following questions with your students:

  • Were you able to guess your partner’s animal? (not all students will be able to guess what the other student’s animal was)
  • What kinds of questions were most helpful in trying to identify your partner’s animal?  What kinds of questions were not helpful?
  • Did you find that it was better if your questions were asked in a particular order?
  • Did you have any difficulties in guessing the other player’s animal?  What made it difficult?

Part II. Introduction

Now, what if you were a scientist and you needed to identify an organism that you weren’t familiar with?  This is when someone may use a dichotomous key.  Using a dichotomous key is similar in some ways to playing “Guess Who?” The difference is that when you use a dichotomous key, you usually have a specimen in front of you and you are the one trying to identify it.  The couplets on a dichotomous key allow you to narrow down the options of what animal (or plant, etc) your specimen may be.   

  • Explain to students that a dichotomous key is a useful tool used to help identify organisms.
  • Explain that a dichotomous key works by using a series of paired statements, known as couplets. Each statement leads the user to another set of couplets until they reach the name of the specimen.


Print out enough copies of the Key to the Animals of the California Coast Exhibit for each student to have their own or for students to work in pairs. 


  1. Hand out the Key to the Animals of the California Coast Exhibit to students.  Have students look over the key.
  2. Explain to students what a dichotomous key is and what it is used for. 
  3. Tell students that they will be using the key at the California Academy of Sciences to identify animals in the California Coast Exhibit, but that they will first be practicing in the classroom.
  4. Put up one of the pictures for students to see (you can either project the image or print it).  Work together through the key, as a class, to identify the animal in the photo.
  5. With your class, work to identify several of the animals in the sample images using the Key to the Animals of the California Coast Exhibit.
  6. If you are unable to take your students to the California Academy of Sciences, you may simply use the key to identify animals from the powerpoint of images from animals in the California Coast Exhibit in your classroom.

During your visit


  • Print out enough copies of the Taxonomist for a Day for each student to have their own.
  • Print out enough copies of the Key to the Animals of the California Coast Exhibit for each student to have their own or for students to work in pairs.  Depending on the size of your group, you may want to break up into different sections so that not all of the class is crowding around the California tank at once.



  1. Bring students to the California Coast exhibit, and explain that they will be using their new dichotomous key skills to identify animals in the exhibit.
  2. Give your students a copy of the Key to the Animals of the California Coast Exhibit.  Have students work to identify at least four different animals in the tank.  To make sure that students actually used the key to identify the animals, have them fill out the Taxonomist for a Day worksheet.


Have your students answer the questions on the back of the Taxonomist for a Day worksheet. 

Back at School

It may be beneficial to engage the class in a class discussion based on these questions after you return to your classroom.

  • Why is it important for scientists to be able to properly identify different species? (Scientists need baseline data to know which species live in a particular area.  Without this information, scientists would not be able to document change of an ecosystem over time, or wouldn’t recognize whether a species is native or non-native. Proper identification also helps scientists to document when extinctions occur.)
  • Why might you have been unable to identify a specimen with your key? (There are many possibilities here. The user may have made an error at one of the couplets, and advanced to the wrong number couplet.  Occasionally, some keys can be ambiguous or require skills or knowledge of scientific terms beyond those the user possesses.  It is also a possibility that the specimen may be a new and undescribed species, or the key is written to identify species only found in a specific geographic area, e.g. “The Fishes of San Francisco Bay.”  In this activity, the key was designed specifically for the exhibit. If you are unable to identify your specimen, it may be because of user error, or perhaps because additional animals have been added to the tank after this key was written.)
  • How successful do you think you would be if you took this Key to the Animals of the California Coast and tried to use it in the field?  Explain your answer. (There are many species that are found in the California marine environment that are not found in the CAS exhibit.  Since the key was designed specifically for the species in the CAS exhibit, trying to identify other animals using the key might lead you to an incorrect identification, or a dead end.)
  • What animals or kinds of animals are found on the California Coast that are not found in our exhibit?  Why do you think these are not on display in the Steinhart Aquarium?  (The Academy specifically excludes many predators from the exhibit.  These predators would be problematic since they might prey on other animals in the tank.  In their natural environment, predators play an important role of maintaining the populations of their prey.  If these species disappeared from the coast ecosystem, their populations of prey animals would increase in abundance to a level that would lead to imbalances at lower levels in the food web.)
  • What would happen if the following animals/types of organisms disappeared from their natural ecosystem?
    • Predators- The populations of prey of these predators would increase in number and those animals would over-exploit their resources.
    • Kelp/algae- There wouldn’t be food for herbivores or habitat for many animals.
    • Scavengers/decomposers- There would be a build-up of detritus, and nutrients would not flow through the ecosystem properly.
  • What types of threats do these organisms face? What would happen if those species disappeared from their natural ecosystem? (Threats to coastal marine animals include over-harvesting, pollution and nutrient input resulting from agriculture, climate change, coastal development, etc.   If these species disappeared, ecosystems could collapse which would impact tourism, seafood resources, water quality, etc.)


  • This version of “Guess Who?” was designed in a way that just about anyone could play, without having much prior knowledge about the animals involved.  If you wanted to, you could introduce students to the different parts of the animals, and have them playing the game using vocabulary such as column, tentacles, fins, etc. (see Vocabulary section at the beginning of the lesson).
  • Have students create their own dichotomous key for identifying something of their choosing.  Students could choose a set of shapes or different inanimate objects and create a key to identify them. 



  • Schuh, R.T. (2000).  Biological Systematics Principles and Applications. New York: Cornell University Press.
  • Light, Sol Felty, (1886-1947)   The Light and Smith manual : intertidal invertebrates from central California to Oregon / edited by James T. Carlton.  Berkeley, Calif.: University of California Press, c2007.
  • Hickman, C.P., Roberts L.S. and Larson A. (2003). Animal Diversity 3rd Ed. New York: McGraw-Hill.

California Content Standards

Grade Seven

Life Sciences: Evolution

  • 3. a. Students know both genetic variation and environmental factors are causes of evolution and diversity of organisms.

Investigation and Experimentation

  • 7a. Select and use appropriate tools and technology (including calculators, computers, balances, spring scales, microscopes, and binoculars) to perform tests, collect data, and display data.

Grades Nine though Twelve

Life Sciences: Ecology

  • 6a. Students know biodiversity is the sum total of different kinds of organisms and is affected by alterations of habitats.

Life Sciences: Evolution

  • 8b. Students know a great diversity of species increases the chance that at least some organisms survive major changes in the environment.

Investigation and Experimentation

  • 1.a. Select and use appropriate tools and technology (such as computer-linked probes, spreadsheets, and graphing calculators) to perform tests, collect data, analyze relationships, and display data.



Biodiversity encompasses the variety of living things from the level of DNA to the level of species and ecosystems. Humans and all living things depend on the services that biodiversity provides, such as food, energy, material resources, clean air and water. Studying biodiversity is important for monitoring the health of ecosystems, humans and the planet.  When we know about species that live in a particular area, we can take steps to protect these precious resources.

Biologists at the California Academy Sciences document the biodiversity of our planet.  They study the natural history of many different types of organisms, including where the organisms live, their behavior, and the role they play in ecosystems.  They identify species, some of them new to science, and name, describe and classify those organisms.  This field is referred to as taxonomy.  Taxonomic studies are the first step towards understanding the evolutionary relationships among different organisms, an area of biology known as systematics.

One of the fundamental skills of a taxonomist or systematist is the ability to identify species.  If you were a taxonomist, how would you go about identifying an organism you were not familiar with? Identifying organisms requires careful observation. Often, taxonomists must search through the scientific literature for species descriptions, or use DNA sequences to identify species.  Another tool that taxonomists use is a dichotomous key. A dichotomous key works by using a series of paired statements, known as couplets. Each statement leads the user to another set of couplets until the organism is identified.  It is important to note that there are many groups of organisms for which keys have not yet been written. 

A dichotomous key is similar to playing a game of “20 questions” or the game “Guess Who?” in that both require answering a series of questions to reach an answer or solution. These games are a great way to introduce students to the concept of a dichotomous key and how it works.  This can also get students thinking about how scientists study the evolutionary histories of organisms based on shared characteristics.

In this lesson, your students will become familiar with how a dichotomous key works by playing a special version of the game “Guess Who?” Students will then identify animals using a dichotomous key designed specifically for the California Coast exhibit at the California Academy of Sciences (CAS).  The exhibit itself has only a small selection of all of the species that are found in the California coastal marine environment.  This is because many species are difficult to maintain in captivity.  In addition, the biology of many species is still poorly known, making it a challenge to provide the proper conditions and food to maintain these species in captivity.  Furthermore, many animals are unsuitable for display because of the large tank sizes needed to keep them.

Please note that this key was designed specifically for the California Coast exhibit.  Many of the animals in the tank exhibit variation in coloration and appear different than how they would look in the wild.  Diet can affect the coloration of the fish, and lighting in the exhibit can alter the way the organisms’ colors would look under natural lighting conditions.


Share how you adapted this activity for your grade level. Or, ask us a question!
If you used this lesson, give your star rating above.

comments powered by Disqus